Since 1851, when the standard was set at 37 degree Celsius or 98.6 degree Fahrenheit, the average human body temperature has steadily declined. Researchers studied three data bases - 23,710 readings obtained between 1862 to 1930 in veterans of the Civil War; 15301 records in a national health survey from 1971 to 197, and 1,50,280 entries in a Stanford University database from 2007 to 2017 – to come to the conclusion that the new normal body temperature in humans could be 97.5 degree F.

The researchers observed that the body temperature of men born in the 2000s was on an average 1.06 degrees lower than that of men born in the early 1800s. A similar reduction was observed in women too. Body temperature of women born in 2000s is on an average 0.58 degrees F lower than that of women born in the 1890s.

Difference in measurement technique and equipment used do not explain the decrease in mean body temperature. The decline was evident even within each database, year by year, and the drop between the two modern databases, given the equipment and techniques were the same, was identical.